DoF and a mirror

[Josh66]

Do the same thing, but without the mirror. (I'm just making these numbers up, but you get the point) - say the mirror is 10 feet in front of you, and the dwarves are 20 feet behind you. Camera is aimed at the mirror.

(I am also assuming that the lens you're using has a distance scale on it) - Focus on the mirror. The surface of the mirror is in focus, but the dwarves are not, because they are another 30 feet away. Now focus on the dwarves - the scale on the lens should be showing that's it's focused at 30 feet.

 

[hamlet]

That checks out. But i'm glad i asked this question, because now i've learned how to override my maximum close focus. Something good did come out of this after all.

 

[amolitor]

This is not obvious, hence the need to experiment.

Now think about how a ray of light to be focused actually behaves. It actually DOES behave a bit like a window to another dimension, a mirror world that is a mirror image of our own, but with the same distances and so on involved.

 

[Josh66]

(Drawing not to scale.)

 

[Bitter Jeweler]

That checks out. But i'm glad i asked this question, because now i've learned how to override my maximum close focus. Something good did come out of this after all.

You've learned nothing.

 

[480sparky]

.......because now i've learned how to override my maximum close focus........

Huh?

 

[Josh66]

That checks out. But i'm glad i asked this question, because now i've learned how to override my maximum close focus. Something good did come out of this after all.

You've learned nothing.

That might be a little bit harsh. I'm pretty sure I know what he means, but he might not have expressed it in the best way.

Using a mirror, you can make an object that is physically close to you optically far from you. You are not really changing any of the distances though (since the light path is what we were measuring all along), just modifying the path it takes.

 

[Bitter Jeweler]

That checks out. But i'm glad i asked this question, because now i've learned how to override my maximum close focus. Something good did come out of this after all.

You've learned nothing.

That might be a little bit harsh. I'm pretty sure I know what he means, but he might not have expressed it in the best way.

Using a mirror, you can make an object that is physically close to you optically far from you. You are not really changing any of the distances though (since the light path is what we were measuring all along), just modifying the path it takes.

And that minimum focusing distance will never change, so how does the mirror help?

 

[Josh66]

You've learned nothing.

That might be a little bit harsh. I'm pretty sure I know what he means, but he might not have expressed it in the best way.

Using a mirror, you can make an object that is physically close to you optically far from you. You are not really changing any of the distances though (since the light path is what we were measuring all along), just modifying the path it takes.

And that minimum focusing distance will never change, so how does the mirror help?

Well, it doesn't change the minimum focusing distance, if that's what you mean. That is a 'feature' of the lens and cannot be changed. What the mirror does is modify the camera-to-subject distance. If you are holding the camera, aiming at yourself in a mirror that is 5 feet away, the "subject" is 10 feet away.

You're not focusing on the surface of the mirror, but your reflection in it.

edit
Lets say that the minimum focusing distance of your lens is 2 feet. The mirror is 1.5 feet away. Too close to focus. But the "subject" (you) is 3 feet away (the distance to the mirror and back) - within focusing range of the lens.


...Don't make me post another crappy drawing, lol. If I have to do another one, it will be with pen and paper and get scanned. I can't draw for **** with a mouse.

You'll figure it out in a matter of seconds, but this is the general idea:

 

[pgriz]

Say Hamlet, while we're on the subject of mirrors - if a mirror reverses right and left, why doesn't it reverse top and bottom?

 

[Josh66]

The main part of that question is IF.
(Left and right are not reversed.)

 

[pgriz]

So, when you stand face to face with a person, their right side is on your left. When you stand with the mirror in front of you, your left is now on the mirror image right. How come?

 

[Josh66]

It's reversed front-to-back, not left -to-right.

You might have different mirrors than me , but when I move my right arm, the arm on the right side moves in the mirror.

 

[pgriz]

Josh! Dang it, man! Stop clarifying the murk! This was for Hamlet! :mrgreen:

 

[hamlet]

I'm pleading the fifth or section 7.